Image processing apparatus and image processing method within inclination angle correction

ABSTRACT

An image processing apparatus has an area sensor unit that reads image data corresponding to a plurality of frames shifted from each other by a shift of less than one pixel, an inclination angle acquiring unit that acquires an inclination angle with respect to a reference installation position of the area sensor, an angle correcting unit that corrects the inclination of the image data corresponding to a plurality of frames read by the area sensor unit by using the acquired inclination angle, and a high-resolution conversion unit that provides image data the resolution of which is higher than the resolution of the read image data by using the image data corresponding to a plurality of frames the inclination of which has been corrected by the angle correcting unit to perform interpolation processing.

TECHNICAL FIELD

The present invention relates to an image processing apparatus and animage processing method for reading an original document image andprocesses the image.

BACKGROUND ART

In recent years, it is an increasing trend that offices are networkedand documents handled there are digitized and colored. Digitizationallows documents to be readily processed and transferred for efficientoperations. Colorization allows good-looking, effective documents to becreated. As documents are increasingly digitized and colored,multifunction peripherals (MFPs), which are image processing apparatus,are required to effectively capture and output generated image data.

The configuration of an image processing apparatus including an imagereader is an element most closely associated with one of originaldocument image capturing performance and image quality of output imagesin a copy mode. The reader in an image processing apparatus is adaptedto include a reduction optical system and a proximity optical system.

The reading resolution of the above optical systems depends on pixelsensors arranged in a primary scan direction. There is a technologycalled “super-resolution processing” as a process of improving theresolution independent of the number of pixel sensors arranged in aprimary scan direction.

While the technology will be described later, the super-resolutionprocessing involves using multiple sets of image data read at theresolution of the sensors provided in the reader to significantlyimprove the resolution of an output image.

Using the super-resolution processing technology allows image datacorresponding to a plurality of frames, for example, read at aresolution of 300 dpi to be converted into image data having aresolution of 1200 dpi.

Processes involved in the super-resolution processing in whichhigh-resolution image data that cannot be obtained by a reader in animage processing apparatus is produced by using multiple sets of imagedata are described in detail in WO2004/068862.

Japanese Patent Application Laid-Open No. 2006-092450 describeshigh-resolution processing in which the number of images used as a baseof a combined image is controlled according to the image size. Thistechnology involves increasing the number of images to be combined whenthe image size is small.

To carry out the super-resolution processing described above, however,first of all, it is necessary to prepare successive sets of image datacorresponding to a plurality of frames obtained by reading an originaldocument image with the reading position minutely shifted from one tothe other with reference to one-frame image data read at the resolutionof sensors provided in an image processing apparatus including a reader.

That is, it is necessary to prepare successive sets of image datacorresponding to a plurality of frames obtained by slightly shifting thepositions of pixels to be read in the primary and/or secondary scandirections from reference image data.

Further, when the image data corresponding to a plurality of frames isobtained, the position at which the original document image is read by asensor to acquire image data is shifted from the position at which theoriginal document image is read by the adjacent sensor to acquire imagedata. The shift needs to be smaller than one pixel (sub-pixel) in theprimary and/or secondary scan directions.

The greater the resolution of image data generated by thesuper-resolution processing, the greater the number of necessary imagedata frames in the image data read at the resolution of the sensorsprovided in the apparatus.

Performing the super-resolution processing in an image processingapparatus thus allows a low-resolution reader to provide ahigh-resolution image. To this end, however, it is necessary to satisfythe conditions described above.

In general, however, the reader in a multifunction peripheral, ascanner, and other image processing apparatus uses a line sensor.

That is, the number of frames read in a single reading action is one.

Further, the reader described above reads an original document image byusing a group of pixel sensors horizontally arranged in the primary scandirection with the distance between pixels being equal to an integralmultiple of the size of a pixel. It is thus disadvantageously notpossible to read the original document image by minutely (on a sub-pixelbasis) shifting the positions of pixels to be read in the primary scandirection.

DISCLOSURE OF THE INVENTION

To solve the above problems, an image processing apparatus of thepresent invention comprises:

an area sensor unit that reads image data corresponding to a pluralityof frames shifted from each other by a shift of less than one pixel;

an inclination angle acquiring unit that acquires an inclination anglewith respect to a reference installation position of the area sensor;

an angle correcting unit that corrects the inclination of the image datacorresponding to a plurality of frames read by the area sensor unit byusing the inclination angle acquired by the inclination angle acquiringunit; and

a high-resolution conversion unit that provides image data theresolution of which is higher than the resolution of the pixel sensorsby using the image data corresponding to a plurality of frames theinclination of which has been corrected by the angle correcting unit toperform interpolation processing.

The present invention can provide an image processing apparatus capableof performing super-resolution processing in which multiple sets oflow-resolution image data read by a sensor fixed in an inclined positionwith respect to a reference installation position are used to provide ahigh-resolution image.

Even image data read at a low resolution can thus be output as ahigh-resolution image.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the configuration of a reader in the presentinvention.

FIG. 2 illustrates the configuration of an MFP 101.

FIG. 3 illustrates the hardware configuration of a video controller 201.

FIG. 4 is a block diagram illustrating an example of the configurationof a scanner image processor 312.

FIG. 5 is a block diagram illustrating an example of the configurationof a printer image processor 315.

FIG. 6 illustrates an example of the configuration of software.

(a), (b) and (c) of FIG. 7 illustrate a configuration diagram of areduction optical system in a conventional MFP.

(a), (b) and (c) of FIG. 8 illustrate a super-resolution processing.

(a), (b), (c), (d), (e) and (f) of FIG. 9 illustrate a super-resolutionprocessing.

(a), (b), (c) and (d) of FIG. 10 illustrate a super-resolutionprocessing.

FIG. 11 describes super-resolution processing in detail.

FIG. 12 describes super-resolution processing in detail.

FIG. 13 illustrates the configuration of an area sensor.

FIG. 14 illustrates an original document image to be read by the areasensor.

(a), (b), (c), (d) and (e) of FIG. 15 illustrate how to acquire lineimage data.

(a), (b), (c), (d) and (e) of FIG. 16 illustrate how to acquire lineimage data.

(a), (b), (c), (d) and (e) of FIG. 17 illustrate how to acquire lineimage data.

(a), (b), (c), (d) and (e) of FIG. 18 illustrate how to acquire lineimage data.

(a) and (b) of FIG. 19 illustrate image data read by line sensors in anarea sensor.

(a) and (b) of FIG. 20 illustrate a configuration diagram when an areasensor is fixed in an inclined position.

(a), (b), (c), (d) and (e) of FIG. 21 illustrate how an inclined areasensor acquires line image data.

(a), (b), (c), (d) and (e) of FIG. 22 illustrate how an inclined areasensor acquires line image data.

(a), (b), (c), (d) and (e) of FIG. 23 illustrate how an inclined areasensor acquires line image data.

(a) and (b) of FIG. 24 illustrate image data read by line sensors in aninclined area sensor.

FIG. 25 is a flowchart describing a copy process of an MFP.

FIG. 26 illustrates an example of a test chart.

(a) and (b) of FIG. 27 illustrate a diagram describing a concept of amethod for detecting the inclination of an area sensor.

FIG. 28 is a flowchart describing a process of detecting the inclinationof an area sensor.

FIG. 29 is a diagram describing a process of acquiring an angle by usingan area sensor to read a vertical line having a width corresponding to asingle pixel and finding an edge of the line.

BEST MODES FOR CARRYING OUT THE INVENTION

(Description of the Configuration of a Reader)

FIG. 1 illustrates the configuration of a reader. FIG. 1 illustrates anexample of a reader in an image processing apparatus to which thepresent embodiment is applied.

FIG. 1 illustrates a body 101 of the reader, an ADF 102 that holds downan original document 103 and feeds the original document to an originaldocument reading position when the original document is scanned, and aglass platen 104 on which the original document 103 is placed forreading of an original document image on the original document.

A unit 105 includes a reading device that reads the original documentimage 103, that is, a device that images the original document image. Alight source 106 is a xenon lamp or other white-light sources. Mirrors107 to 111 serve to reflect the light that is emitted from the lightsource 106 and illuminates the image, and deliver the reflected light tothe imaging device. A lens 112 focuses the light reflected off themirror 111 to match the size of the light with the width of the imagingdevice. FIG. 1 also illustrates the imaging device as an element 113.

FIG. 2 illustrates an example of the configuration of the imageprocessing apparatus in the present embodiment. The image processingapparatus is formed in the body 101 of the reader illustrated in FIG. 1.In FIG. 2, a video controller 201 controls the image processingapparatus illustrated in FIG. 1 and has the hardware configurationillustrated in FIG. 3, which will be described later. A scanner 202optically reads an original document image under the control of thevideo controller 201, and a printer 203 prints an input image on arecording medium under the control of the video controller 201.

The printer 203 will be described with reference to anelectrophotographic laser beam printer. A finisher 204 is connected tothe printer 203. The finisher 204 can staple a plurality of recordingmedia (printing sheets, for example) together that have been output fromthe printer 203.

The finisher 204 staples the output recording media and carries outother processes under the control of the video controller 201. A network(Ethernet®, for example) interface 206 provides two-way communicationwith the video controller 201 via the interface 206. The functions to beprovided can be acquired by externally querying an overall managementmanager (supervisor), which will be described later, via the interface206.

The functions to be provided include the number of maximum copies, thetype of the finisher, supported PDLs, and the number of specifiableoutput BINs.

FIG. 2 also illustrates an operation section 205, which is a userinterface (UI). The operation section 205 includes an LCD display and akeyboard, displays information from the video controller 201, anddelivers an instruction from a user to the video controller 201.

The configuration of the MFP connected to the network 206 will bedescribed in detail.

(Description of the Configuration of the Video Controller 201)

FIG. 3 illustrates an example of the hardware configuration of the videocontroller 201 illustrated in FIG. 2.

The video controller 201 is not only electrically connected to thescanner 202 and the printer 203 but also connected to a print server(not illustrated) and an external apparatus via a network 21 and a WAN22. It is thus possible to input and output image data and deviceinformation.

A CPU 301 carries out overall control of access to a variety ofconnected devices and also carries out overall control of a variety ofprocesses performed in the video controller 201, for example, based on acontrol program stored in a ROM 303.

A RAM 302 is a system work memory used by the CPU 301 to operate, andtemporality stores image data. The RAM 302 includes an SRAM that holdsstored information even after the power is turned off and a DRAM thatloses stored information after the power is turned off.

The ROM 303 stores a program that boots the apparatus and otherprograms. An HDD 304 is a hard disk drive and can store system softwareand image data.

An operation section I/F 305 is an interface that connects the operationsection 205 to a system bus 310. The operation section I/F 305 receivesimage data to be displayed on the operation section 205 from the systembus 310 and outputs the image data to the operation section 205. Theoperation section I/F 305 also outputs information input from theoperation section 205 to the system bus 310.

A network I/F 306 is connected to the network 206 and the system bus310, and inputs and outputs information. A modem 307 is connected to aWAN 22 and the system bus 310, and inputs and outputs information. Abinary image rotator 308 converts the direction of image data beforetransmitted. A binary image compressor/expander 309 converts theresolution of image data before transmitted into one of a predeterminedresolution and a resolution that matches the ability of a communicationcounterpart. Compression and expansion will be carried out using JBIG,MMR, MR, MH, or other methods. An image bus 330 is a transmission paththrough which image data is transmitted, and comprised of one of a PCIbus and an IEEE 1394 bus.

A scanner image processor 312 corrects, processes, and edits image datareceived from the scanner 202 via a scanner I/F 311. The scanner imageprocessor 312 determines whether received image data is a color originaldocument image or a monochrome original document image, acharacter-based original document image, a photographic originaldocument image, or other types of original document image. Thedetermination result is imparted to the image data. The impartedinformation is referred to as attribute data. The processes performed inthe scanner image processor 312 will be described later in detail.

A compressor 313 receives image data and divides the image data intoblocks, each of which has a dimension of 32 pixels by 32 pixels. Theimage data having a dimension of 32 pixels by 32 pixels is referred toas tile data. In an original document image (paper-based medium that hasnot yet undergone a reading operation), an area corresponding to thetile data is referred to as a tile image. The tile data has headerinformation including average brightness information in the 32×32 pixelblock and coordinates of the tile image on the original document image.Further, the compressor 313 compresses image data comprised of multiplesets of tile data. An expander 316 expands image data comprised ofmultiple sets of tile data, arranges the image data in a raster format,and sends the resultant data to a printer image processor 315.

The printer image processor 315 receives the image data sent from theexpander 316 and performs image processing on the image data whilereferring to the attribute data imparted to the image data. The imagedata that has undergone the image processing is output to the printer203 via a printer I/F 314. The processes performed in the printer imageprocessor 315 will be described later in detail.

An image converter 317 performs predetermined conversion processes onimage data. The image converter 317 includes the following processors.

An expander 318 expands received image data. A compressor 319 compressesreceived image data. A rotator 320 rotates received image data. A scaler321 performs resolution conversion (converting 600 dpi into 200 dpi, forexample) on received image data. A color space converter 322 convertsthe color space of received image data. The color space converter 322can perform known background skip, known LOG conversion (RGB→CMY), andknown output color correction (CMY→CMYK) using one of a matrix and atable. A binary/multi-value converter 323 converts received binary imagedata into 256-grayscale image data. In contrast, a multi-value/binaryconverter 324 converts received 256-grayscale image data into binaryimage data, for example, by using error diffusion method.

A combiner 327 combines two sets of received image data to generate asingle set of image data. Examples of a method for combining two sets ofimage data include a method in which brightness values of pixels to becombined are averaged to produce a combined brightness value and amethod in which the brightness value of the pixel having a brighterlevel chosen from pixels to be combined is defined as the brightnessvalue of the combined pixel. It is also possible to employ a method inwhich the pixel having a darker level chosen from pixels to be combinedis defined as the combined pixel. It is further possible to employ amethod in which the OR operation, AND operation, exclusive-OR operation,or other operations on pixels to be combined is used to determine thecombined brightness value. All of the combination methods describedabove are known in the art. A thinning section 326 performs a thinningprocess on received image data for resolution conversion to producesmaller-sized image data by multiplying ½, ¼, ⅛ or other factors. Amoving section 325 adds a margin to received image data or removes amargin from received image data.

An RIP 328 receives intermediate data generated based on PDL code datasent from the print server (not illustrated) or other components,produces (multi-value) bitmap data, and compresses the bitmap data in acompressor 329.

(Detailed Description of the Scanner Image Processor 312)

FIG. 4 illustrates an example of the internal configuration of thescanner image processor 312 illustrated in FIG. 3.

The scanner image processor 312 receives image data comprised of 8-bitRGB brightness signals. A masking processor 401 converts each of thebrightness signals into a standard brightness signal independent offilter colors of a CCD.

A filter processor 402 arbitrarily corrects the spatial frequency ofreceived image data. The processor carries out an operation, forexample, using a 7×7 matrix on the received image data. In a copier, theuser can operate the operation section 205 to select, as a copy mode, acharacter mode, a photograph mode, and a character/photograph mode. Whenthe user selects the character mode, the filter processor 402 applies acharacter filter to the entire image data. When the user selects thephotograph mode, the filter processor 402 applies a photograph filter tothe entire image data. When the user selects the character/photographmode, a filter is switched for each pixel according to acharacter/photograph determination signal (part of attribute data),which will be described later. That is, it is determined whether thephotograph filter or the character filter is applied for each pixel. Thephotograph filter has a coefficient set to smooth only high frequencycomponents in order to reduce graininess of an image. On the other hand,the character filter has a coefficient set to enhance edges in arelatively strong manner in order to sharpen characters.

A histogram generator 403 performs sampling to produce brightness dataof the pixels that form received image data. More specifically,brightness data in a rectangular area defined by start and end pointsspecified in the primary and secondary scan directions is sampled atfixed intervals in the primary and secondary scan directions. Ahistogram data is then generated based on the sampling result. Thegenerated histogram data is used, when background skip is performed, toestimate the background. An input-side gamma corrector 404 converts thehistogram data into nonlinear brightness data, for example, using atable.

A color/monochrome determination section 405 determines whether each ofthe pixels that form received image data has a chromatic color or anachromatic color, and imparts the determination results to the imagedata as color/monochrome determination signals (part of attribute data).

A character/photograph determination section 406 determines whether eachof the pixels that form the image data forms a character, a halftonedot, a character on halftone dots, or a solid image based on the pixelvalue of each pixel and the pixel values of surrounding pixels aroundthe pixel. A pixel that belongs to none of the above pixels forms awhite area. The determination results are then imparted to image data ascharacter/photograph determination signals (part of attribute data).

A color reproduction range determination section 407 determines a colorrange of received image data, and acquires a color reproduction rangespecified in a transfer job based on color reproduction rangeinformation for each device returned therefrom.

(Detailed Description of the Printer Image Processor 315)

FIG. 5 illustrates an example of the internal configuration of theprinter image processor 315 illustrated in FIG. 3.

A background skipping processor 501 uses the histogram generated in thescanner image processor 312 to skip a background color of image data. Amonochrome generator 502 converts color data into monochrome data. A Logconverter 503 performs brightness/density conversion. The Log converter503 converts, for example, RGB input image data into CMY image data. Acolor conversion/compression processor 504 responds to a query of thecolor reproduction range from any of other devices and produces acompression table from colorimetric information to determine the colorreproduction range. The color conversion/compression processor 504 alsoperforms data compression according to a specified color reproductionrange from any of other devices until the data compression is performedacross the specified range. An output color corrector 505 performsoutput color correction. For example, CMY input image data is convertedinto CMYK image data by using one of a table and a matrix. Anoutput-side gamma corrector 506 performs correction in such a way that asignal value input to the output-side gamma corrector 506 isproportional to a reflection density value after a copy output process.A coded image combiner 508 uses image data produced by ameta-information image generator (not illustrated) to combine the imagedata with meta-information embedded copy-forgery-inhibited pattern imagedata produced in a copy-forgery-inhibited pattern image processor (notillustrated). A halftone corrector 507 performs halftone processingaccording to the number of grayscales in the output printer. Forexample, the halftone corrector 507 converts received image data havinga large number of grayscales into binary image data, 32-value imagedata, or image data having other number of values.

The scanner image processor 312 and the printer image processor 315 canalso output received image data as it is. Thus forwarding data as it isthrough a certain processor is hereinafter referred to as “forward datathrough a processor.”

(General Description of the Software Configuration)

A description will be made of the configuration of software (programmodules) stored in the HDD 304 in the video controller 201, loaded tothe memory (RAM) 302, and executed by the CPU 301.

FIG. 6 illustrates an example of the software configuration in thepresent embodiment. In FIG. 6, a UI driver 601 controls the operationsection 205 illustrated in FIG. 6. A user I/F manager (control program)603 acquires input information input by the user through the keyboard ofthe operation section 205 via the UI driver 601 and delivers the inputinformation to an overall management manager (supervisor) 605 thatcarries out overall management of the action of the video controller201. The user I/F manager 603 also acquires processing results obtainedin the video controller 201 via the overall management manager 605 andinstructs the operation section 205 to display the processing results onthe LCD display.

FIG. 6 also illustrates a network I/F driver (control program) 602.

The network I/F driver 602 controls the network I/F 306 to process aphysical layer (physical packet) in the network, that is, extract atransport packet from a physical packet and produce a physical packetfrom a transport packet.

A TCP/IP and UDP/IP communication module 604 delivers the transportpacket information output from the network I/F driver 602 to the overallmanagement manager 605. The TCP/IP and UDP/IP 604 also produces atransport packet from the information from the overall managementmanager 605 and outputs the transport packet to the network 206 via thenetwork I/F driver 602.

The overall management manager 605 (Supervisor) performs overallmanagement of the action of the video controller 201 and holdsidentification information and other data (attribute table) of theapparatus in the HDD 304. The overall management manager 605, forexample, refers to processing performance and other data held in a scanjob manager 606, a copy job manager 607, and a print job manager 608,instructs the managers to change their processing performance and otherdata, and distributes jobs (print job, copy job, scan job).

The print job manager 608 manages printer resources and controls jobexecution. The printer image processor 315 performs image processing onan output image in response to a request from the print job manager 608.The print job manager 608 also communicates with a printer controller(not illustrated) that operates the printer via the printer I/F 314 forprinter control. The copy job manager 607 manages copy resources andcopy jobs. The scanner job manager 606 manages scanner resources andcontrols job execution. The scanner image processor 312 performs imageprocessing on an input image in response to a request from the scannerjob manager 606. Further, the scan job manager 606 communicates with ascanner controller (not illustrated) that operates the scanner via thescanner I/F 311 for scanner control.

(Description of an Image Reader in a Typical Multifunction Peripheral)

A description will be made of an example of a reduction optical systemas the configuration of an image reader in a typical image processingapparatus with reference to (a), (b) and (c) of FIG. 7.

In a typical high-performance reader, a reduction optical system isoften used to keep the reading speed, the reading resolution, the imagequality of read image data, and other performance.

A device used in a reading portion of the reduction optical system is aCCD (Charge Coupled Device) in many cases.

(a) of FIG. 7 illustrates the configuration of an image reader using areduction optical system.

(a) of FIG. 7 illustrates a body 701 of the reader, and an ADF (AutoDocument Feeder) 702 that holds down an original document 703 and feedsthe original document to an original document reading position when theoriginal document scanned.

(a) of FIG. 7 also illustrates a glass platen 704 on which the originaldocument 703 is placed for reading of an original document image on theoriginal document, and a unit 705 including a reading device that readsthe original document image, that is, a device that images the originaldocument image.

A light source 706 is typically a xenon lamp or other white-lightsources. Mirrors 707 to 711 serve to reflect the light that is emittedfrom the light source 706 and illuminates the original document image,and deliver the reflected light to an imaging device.

A lens 712 focuses the light coming from the original document image andreflected off the mirror 711 to match the size of the light with thewidth of the imaging device.

The imaging device 713 is comprised of a CCD in a reduction opticalsystem.

The process of reading an original document image in the reductionoptical system will now be described. The light that is emitted from thelight source 706 and illuminates the original document image 703 isreflected off the original document image placed on the glass platen 704and received by the mirror 707. The intensity of the light reflected offthe mirror 707 depends on the original document image, and the brighterthe original document image, the higher the light intensity.

That is, when the color of the original document image is white, whichhas a high reflectance, the light intensity is most intense. The lightreceived by the mirror 707 is sequentially reflected off the mirror 708,the mirror 709, the mirror 710, and the mirror 711, and then output tothe lens 712.

The lens 712 focuses and outputs the light reflected off the mirror 711in such a way that the focused light matches the width of the imagingdevice 713.

A reduction optical system is characterized by the configuration inwhich the light reflected off an original document image is reflectedoff a plurality of mirrors, focused by a lens in the final stage, andinput to an imaging device.

In a reader using a reduction optical system, the reason why a pluralityof mirrors is used to reflect the light is that an optical path having acertain length is necessary to match the size of the light with thewidth of a CCD.

For example, an optical path necessary to focus optical data of anoriginal document image onto a CCD having a width of 50 mm is at leastapproximately 200 mm in length.

A reduction optical system thus requires an optical path lengthaccording to the size of the imaging device, but the reduction opticalsystem has excellent reading characteristics.

Specifically, even when the original document image 703 is not perfectlyin contact with the glass platen 704, the original document image can beread sharply. The distance necessary to achieve a sharp focus is calledthe depth of field. Even when the original document image 703 is notperfectly in contact with the glass platen 704, a greater depth of fieldprevents problems in reading the original document image from occurringto some extent.

(b) and (c) of FIG. 7 show an example of the configuration of theimaging device 713, that is, a CCD device.

(b) of FIG. 7 illustrates an example of a three-line sensor with theprimary and secondary scan directions being the horizontal and verticaldirections, respectively. In (b) of FIG. 7, line sensors 713 a, 713 b,and 713 c read three color signals that form a color image, and each ofthe lines sensors can read line data formed of H pixels in the primaryscan direction.

The line sensors that read the color signals contain pixel sensors 713d, 713 e, and 713 f. The pixel sensors are successively arranged in thehorizontal direction for each of the color signals to be read.

The reading resolution of the CCD device depends on the number of pixelsensors arranged for each of the color signals. That is, a larger numberof pixels H allow image data to be read at a higher resolution.

For example, when a CCD has a reading resolution of 600 dpi, thedistance between adjacent pixel sensors is determined based on theresolution of 600 dpi.

The reading resolution, that is, the number of pixel sensors directlyaffects the unit price of a CCD.

That is, to read image data at a high resolution, a reader must use aCCD having a large number of pixel sensors even when such a CCD isexpensive in unit price.

A CCD device is further characterized in that line sensors that readcolor signals are spaced apart.

For example, assume that the line sensor 713 a includes a filter used toread red (hereinafter referred to as R) image data. Also assume that theline sensor 713 b includes a filter used to read green (hereinafterreferred to as G) image data.

In this case, there is a physical distance between the line sensor 713 aand the line sensor 713 b implemented as sensors in the imaging device.

Let L (pixels) be the distance described above. There is a shift betweenR image data and G image data read at the same timing, the shiftcorresponding to L pixels in the secondary scan direction.

Similarly, when the line sensor 713 c includes a filter used to readblue (hereinafter referred to as B) image data, there is a shift betweenG image data and B image data read at the same timing, the shiftcorresponding to L (pixels).

The shift between the R image data and the B image data corresponds to 2L (pixels).

The distance L between line sensors that read color signals affects theconfiguration of the image processor in which image data read by thereader is processed.

Typical image processing is not carried out for each of line sensorsthat read RGB color signals but carried out on a pixel basis.

That is, it is necessary to prepare image data in which the distances Lbetween RGB colors are corrected. It is therefore necessary to increasethe memory capacity required for the correction as the distance Lincreases. Further, a mechanical shift generated when the reading deviceunit 705 is in operation does not disadvantageously allow the distance Lbetween line sensors to be a fixed value. The shift causes color shiftwhen read image data is used to form an image, and directly causesdegradation in output image.

To avoid the above problem, the interline distance L in a CCD used in ahigh-performance multifunction peripheral is set to a significantlysmall value corresponding to approximately two lines (pixels).

Next, a four-line-sensor CCD will be described below. (c) of FIG. 7illustrates the configuration of a four-line sensor, again with theprimary and secondary scan directions being the horizontal and verticaldirections, respectively.

In (c) of FIG. 7, line sensors 713 g, 713 h, and 713 i read three colorsignals that form a color image, and each of the lines sensors can readline data formed of H pixels in the primary scan direction.

The line sensors that read the color signals contain pixel sensors 713k, 7131, and 713 m. The pixel sensors are successively arranged in thehorizontal direction for each of the color signals to be read.

A line sensor 713 j reads monochrome image data and can read line dataformed of H pixels arranged in the primary scan direction, as in theline sensors that read a color image. Pixel sensors 713 n read amonochrome image, and are successively arranged in the horizontaldirection.

The four-line sensor differs from the three-line sensor in that sensorsused to read a color image differ from those used to read a monochromeimage, but the basic operation of the four-line sensor is the same asthat of the three-line sensor.

For example, assume that the line sensor 713 g includes a filter used toread R image data.

Similarly, assume that the line sensor 713 h includes a filter used toread G image data, and the line sensor 713 i includes a filter used toread B image data.

In this case, when a color image is read, the line sensors 713 g, 713 h,and 713 i are used to read an original document image.

Since there is the interline distance L between line sensors, the imageprocessor requires, after the image reading stage, a memory forcorrecting the interline distance to generate image data on a pixelbasis.

When a monochrome original document is read, the line sensor 713 j,which is not used to read a color image as described above, is used toread the original document image.

In this case, since the line sensor 713 j is not related to the otherline sensors, the read image data does not undergo interline correctionbut is handled by the image processor after the image reading stage.

In the four-line sensor, as in the three-line sensor, the readingresolution of the CCD device depends on the number of pixel sensorsarranged for each color signal. That is, a larger number of pixels Hallow image data to be read at a higher resolution.

Further, the reading resolution, that is, the number of pixel sensorsdirectly affects the unit price of a CCD, as in the three-line sensor.That is, to read image data at a high resolution, a reader must use aCCD having a large number of pixel sensors even when such a CCD isexpensive in unit price.

As described above, a reader in a typical multifunction peripheralemploys one of the reduction optical system described above and acontact-type optical system.

The fact that the reading resolution depends on the number of pixelsensors arranged in the primary scan direction is common to a reductionoptical system and a contact-type optical system. On the other hand,there is a technology called super-resolution processing.

In the super-resolution technology, multiple sets of image data read atthe resolution of a sensor in a reader are used to significantly improvethe original resolution of the image data.

(Super-resolution Processing)

The super-resolution processing technology will be described withreference to (a), (b) and (c) of FIGS. 8 to 12.

(a) of FIG. 8 illustrates image data to be read by a reader. (b) of FIG.8 illustrates the pixel configuration when the image data is read, forexample, at a resolution of 1200 dpi.

In (b) of FIG. 8, the grid labeled with reference numeral 801 representspixel data at the resolution used when the image data is read.

That is, the distance n between pixels corresponds to the distancebetween adjacent pixel sensors when the image data is read at aresolution of 1200 dpi.

(c) of FIG. 8 illustrates the pixel configuration when the reader readsan image having the same image size at a resolution of 300 dpi. In (c)of FIG. 8, as in (b) of FIG. 8, the grid labeled with reference numeral802 represents pixel data at the resolution used when the image data isread.

Therefore, with reference to the distance n between pixels at aresolution of 1200 dpi, the distance between pixels is as coarse as 4 nwhen the image is read at a resolution of 300 dpi.

Since the reproducibility of an image that has been read is proportionalto the resolution, a direct comparison between the image data read at aresolution of 1200 dpi ((b) of FIG. 8) and the image data read at aresolution of 300 dpi ((c) of FIG. 8) shows that the difference in imagequality is significant.

In the super-resolution technology, multiple sets of image dataequivalent to that illustrated in (c) of FIG. 8 are used to generate theimage data illustrated in (b) of FIG. 8.

Using such a technology allows formation of an image comparable to thatread by a high-resolution device even when the original resolution of areading device is not high.

However, to carry out “super-resolution conversion” to convertlow-resolution image data into one of high-resolution image data andsuper-resolution image data, a certain condition should be satisfied.

According to a certain condition, it is necessary to prepare originaldocument image data corresponding to a plurality of frames obtained byminutely shifting the positions to be read in the primary scan directionand/or the secondary scan direction with reference to original documentimage data read at the resolution of the sensor of the reader.

That is, it is necessary to prepare successive sets of image datacorresponding to a plurality of frames obtained by slightly shifting theposition of the original document image to be read by the sensor in theprimary scan direction and/or the secondary scan direction from thereference image data.

Further, when the image data corresponding to multiple screens (frames)is read, the shift in original document image reading position presentbetween two sets of image data obtained by adjacent sensors needs to besmaller than a single pixel (sub-pixel) in the primary scan directionand/or the secondary scan direction.

In the following description, image data corresponding to a singlescreen (frame) is referred to as “frame image data.” Further, theposition where an original document image is read is referred to as“phase.” The situation in which the phase is shifted is referred to as“the phase is shifted,” and the shift in the position where an originaldocument image is read is referred to as “the shift in phase.”

The low resolution used herein is not limited to 300 dpi, but refers tothe resolution of an image output from the apparatus in a normalprinting process. The primary scan direction used herein is thedirection perpendicular to the direction in which, when an originaldocument image placed on the platen is read by the scanner, the unit 105moves relative to the original document image. As indicated by the arrowA in (a) of FIG. 8, the transverse direction of the read originaldocument image is referred to as the “primary scan direction.”Similarly, the secondary scan direction is the direction parallel to thedirection in which the unit 105 moves. The primary scan direction usedherein is the direction perpendicular to the direction in which, when anoriginal document image placed on the platen is read by the scanner, theunit 105 moves relative to the original document image. As indicated bythe arrow B in (a) of FIG. 8, the longitudinal direction of the readoriginal document image is referred to as the “secondary scandirection.”

It is of course possible to achieve high resolution even when there is ashift in phase only in one of the primary scan direction and thesecondary scan direction.

In this case, however, high resolution is achieved only in the directionin which there is a shift in phase.

The condition necessary for the super-resolution processing will bedescribed with reference to (a), (b), (c), (d), (e) and (f) of FIG. 9and the following figures. (a) of FIG. 9 illustrates the pixelconfiguration when the original document image illustrated in (a) ofFIG. 8 is read at a resolution of 300 dpi. (a) of FIG. 9 is the same as(a) of FIG. 8 illustrating the original document image.

The read image data illustrated in (b) of FIG. 9 is target image data inthe first frame in the super-resolution processing, and is alsoreference image data.

Thereafter, as illustrated in (c) of FIG. 9, the original document imageillustrated in (b) of FIG. 9 is read at a resolution of 300 dpi with thephase of the reference image data shifted by Δx (Δx<4 n) in the primaryscan direction and by Δy (Δy<4 n) in the secondary scan direction.

In this case, the phase of the read image data illustrated in (d) ofFIG. 9 differs from the phase of the original document image and isshifted by Δx in the primary scan direction and by Δy in the secondaryscan direction as illustrated in the figure.

The read image data illustrated in (d) of FIG. 9 is target image data inthe second frame in the super-resolution processing.

Further, as illustrated in (e) of FIG. 9, the original document imageillustrated in (a) of FIG. 9 is read at a resolution of 300 dpi with thephase of the reference image data shifted by Δx′ (Δx′<4 n, Δx<Δx′) inthe primary scan direction and by Δy′ (Δy′<4 n, Δy<Δy′) in the secondaryscan direction.

In this case, the phase of the read image data illustrated in (f) ofFIG. 9 differs from the phase of the original document image and isshifted by Δx′ in the primary scan direction and by Δy′ in the secondaryscan direction as illustrated in the figure.

The read image data illustrated in (f) of FIG. 9 is a target image inthe third frame in the super-resolution processing.

High resolution is achieved by acquiring read low-resolution image datacorresponding to a plurality of frames shifted from one another in termsof phase relative to the reference image data along withsuper-resolution processing.

(a), (b), (c) and (d) of FIG. 10 conceptually illustrates howlow-resolution image data corresponding to three frames is used to formhigh-resolution image data.

(a), (b), (c) and (d) of FIG. 10 illustrates that the super-resolutionprocessing is applied to reference image data illustrated in (a) of FIG.10 and low-resolution image data illustrated in (b) of FIG. 10, (c) ofFIG. 10, . . . corresponding to a plurality of frames shifted from oneanother in terms of phase to provide image data illustrated in (d) ofFIG. 10.

The super-resolution processing performed in this case will be describedin more detail with reference to FIGS. 11 and 12.

FIG. 11 illustrates low-resolution image data to be used in thesuper-resolution processing and image data that has undergone thesuper-resolution processing. FIG. 11 illustrates an original documentimage, reference low-resolution image data F0 obtained by reading theoriginal document image by an area sensor, and target low-resolutionimage data F1 to F3. Each dotted-line rectangle that surrounds theoriginal document image indicates the area when the referencelow-resolution image data F0 is read by the area sensor, and thesolid-line rectangles indicate the areas when the target low-resolutionimage data F1 to F3 is read by the area sensor.

In the present embodiment, the offset amount in the primary scandirection is expressed by “um,” and the offset amount in the secondaryscan direction is expressed by “vm.” The amounts of shift describedabove for the target low-resolution image data Fn (n=1 to 3) areexpressed by “umn” and “vmn.” For example, as illustrated in FIG. 11,the target low-resolution image data F1 is shifted in the secondary scandirection relative to the reference low-resolution image data F0, andthe amounts of shift are expressed as um1 and vm1. Similarly, theamounts of shift for the target low-resolution image data F2 and F3 areexpressed as um2, vm2 and um3, vm3.

The amounts of shift umn and vmn for each target low-resolution imagedata Fn (n=1 to 3) are calculated based on the reference low-resolutionimage data F0 and the target low-resolution image data F1 to F3. Thecalculation is carried out based on inclination information of the areasensor prestored in the ROM 203. FIG. 11 diagrammatically illustratesthat each target low-resolution image data is shifted by a single unitpixel in the present embodiment. In the reading using an area sensor inthe present embodiment, however, there is a shift in phase smaller thana single pixel in the primary and secondary scan directions. Using sucha minute shift allows an image to be converted into a high-resolutionimage as described above.

Therefore, among the pixels that form generated super-resolution imagedata (hereinafter referred to as “generated pixels”), there is a pixelthat does not belong to none of the reference low-resolution image dataand the target low-resolution image data.

Such a pixel is converted into a high-resolution pixel by using imagedata representing pixel values of the pixels that surround the generatedpixel to perform predetermined interpolation processing and combination.Examples of the interpolation processing may include a bi-linear method,a bi-cubic method, and a nearest neighbor method.

For example, interpolation processing using a bi-linear method will bedescribed with reference to FIG. 12. First, a nearest pixel 1802 closestto the position (x, y) of a generated pixel 1801 is extracted from thereference low-resolution image data and the target low-resolution imagedata. From the target low-resolution image data illustrated in FIG. 12,four pixels that surround the generated pixel position are determined assurrounding pixels 1802 to 1805. The data values of the surroundingpixels are weighted by predetermined weights and then averaged toprovide the data value of the generated pixel by using the followingformula.f(x, y)=[|x1−x|{|y1−y|f(x0, y0)+|y−y0|f(x0, y1)}+|x−x0|{|y1−y|f(x,y0)+|y−y0|f(x1, y1)}]/|x1−x0||y1−y0|

Repeating the above processes for each generated pixel position allowsformation of a super-resolution image with the resolution doubledillustrated in FIG. 11. The resolution is not necessarily doubled, butmay be multiplied by a variety of factors. Using a number of data valuesof low-resolution image data in the interpolation processing allowsformation of a more resolved super-resolution image.

(How to Use Area Sensor)

FIG. 1 illustrates an example of the reader in a multifunctionperipheral to which the present embodiment is applied.

FIG. 1 illustrates a body 101 of the reader and an ADF 102 that holdsdown an original document 103 and feeds the original document to anoriginal document reading position when the original document isscanned.

FIG. 1 also illustrates a glass platen 104 on which the originaldocument 103 is placed for reading of an original document image on theoriginal document.

A unit 105 includes a reading device that reads the original documentimage 103, that is, a device that images the original document image.

A light source 106 is a xenon lamp or other white-light sources.

Mirrors 107 to 111 serve to reflect the light that is emitted from thelight source 106 and illuminates the original document image, anddeliver the reflected light to the imaging device.

A lens 112 focuses the light originated from the original document imageand reflected off the mirror 111 to match the size of the light with thewidth of the imaging device.

The imaging device 113 is comprised of an area sensor in the apparatusused in the present embodiment. An area sensor is an imaging device usedin a digital camera and other types of cameras. An area sensor differsfrom the sensor on a line basis described above in that pixel sensorsthat read an original document image are arranged two-dimensionally.

FIG. 13 illustrates the configuration of an area sensor. FIG. 13illustrates an area sensor device 1301.

There are pixel sensors 1302 in the area sensor 1301. The area sensor1301 is comprised of pixel sensors for H pixels in the long-sidedirection and pixel sensors for L pixels in the short-side direction.

The pixel sensor in a single pixel may be equally divided into four toform RGB color pixel sensors.

Further, the number of H pixels may be equal to the number of L pixels(the longer side is equal to the shorter side in length). The resolutionof the area sensor is determined by the distance N between pixelsensors.

An area sensor used in a high-resolution digital camera is comprised ofa significantly large number of pixels as the number of pixel sensors inthe long-side direction and the number of pixel sensors in theshort-side direction. For example, some ten-million-pixel-sized digitalcameras have 3,800 pixels as the pixel sensors in the long-sidedirection and 2,800 pixels as the pixel sensors in the short-sidedirection.

In general, when an area sensor is used in a camera or any other similarapparatus, the area sensor captures input image data as atwo-dimensional area and picks up an image. That is, in a single imagingaction, two-dimensionally arranged pixel sensors are used to pick up animage. When an area sensor device is fixed in the reader, the pixelsensors are disposed in such a way that the pixel sensors are notinclined to convert picked-up image data into an image withoutdistortion in the transverse and longitudinal directions.

The pixel sensors are therefore disposed in such a way that there is nodiagonal misalignment when the picked-up image is reproduced. Forexample, when an area sensor is fixed in a typical camera, image dataread by the line pixel sensors indicated by the black frame 1303 formsthe uppermost end of the imaged object. In this case, the read imagedata is not inclined to the direction in which the line is formed.

Similarly, image data read by the line pixel sensors indicated by theblack frame 1304 is image data in a position different from the positionof the imaged object read by the pixel sensors in the frame 1303, thatis, in a position below the frame 1303 in the vertical direction. Theframe 1305 therefore corresponds to the image data in the position foursteps below the imaging position read by the pixel sensors in the frame1303 in the vertical direction.

As described above, when an area sensor is used in a digital camera, thepixel sensors that form the area sensor pick up images in respectivedifferent positions of the imaged object because image data is picked upin the form of a two-dimensional area.

How to use an area sensor in the apparatus used in the presentembodiment, however, differs from how to use an area sensor in a digitalcamera described above. First, the area sensor illustrated in FIG. 13 isattached in a reference installation position in the reader.

In an image processing apparatus that carries out printing in a typicalmanner, when an original document is placed at a specified position onthe platen 104 in FIG. 1, the light emitted from the light source, whichtranslates under the original document image in the same direction asthe longitudinal direction of the original document image, is directedtoward the original document image, reflected off the original documentimage, and focused onto the sensor. The sensor captures the reflectedlight that is not inclined to the sensor. The reflected light asone-line image data obtained by translating the light source is focusedparallel to the transverse direction (long-side direction) of the sensorillustrated in FIG. 13.

To this end, the sensor is disposed in a position where the sensor cancapture the original document image with almost no inclination. Theposition where the sensor is disposed to achieve such an output of theoriginal document image is referred to as “reference installationposition.”

In the following description, it is assumed, to simplify thedescription, that the sensor is comprised of 20 pixel sensors in thelong-side direction and 10 pixel sensors in the short-side direction.The sensor may of course be structured in such a way that the length inthe long-side direction is equal to the length in the short-sidedirection. It is noted that the number of pixel sensors described aboveis intended to describe the use and configuration of the area sensor inthe present embodiment, and should not be limited to the number ofillustrated pixel sensors.

In practice, the area sensor may of course be adapted by using thenumber of pixel sensors used in a digital camera. The reading unit 105including the area sensor 113 fixed in the reader is moved in thedirection indicated by the arrow illustrated in FIG. 1 to read theoriginal document image 103 placed on the platen 104. That is, thereading line sensors 1304 and 1305, each of which is a set of pixelsensors, are used as the line sensors to carry out reading as describedabove.

How to process image data read by the reading line sensors 1304 and 1305will be described below. FIG. 14 illustrates an image to be read in thefollowing description. That is, the image corresponds to the originaldocument image 103 illustrated in FIG. 1.

The grid illustrated in FIG. 14 corresponds to the resolution of thepixel sensors that form one of the reading line sensors 1304 and 1305.

When the reading unit 105 is driven to move under the platen in thesecondary scan direction, the reading line sensors 1304 and 1305sequentially read image data input thereto.

That is, the portion of the original document image that corresponds tothe line width in the position of the reading unit 105 is successivelyread. The process of reading the original document image will bedescribed.

When the reading unit 105 moves under the platen in the secondary scandirection, the light from the light source impinges on the hatchedportion of the original document image illustrated in (a) of FIG. 15,(a) of FIG. 16, (a) of FIG. 17, and (a) of FIG. 18.

First, at a certain instant, the light from the light source impinges onthe hatched portion in (a) of FIG. 15. The area sensor then senses thelight and detects the portion of the original document image thatcorresponds to the line width, which is the portion on which the lighthas impinged.

For example, at this point, the line sensor 1304 detects image dataillustrated in (b) of FIG. 15. At the same time, the line sensor 1305detects image data illustrated in (c) of FIG. 15.

There is a shift in reading position between the two image data becausethe two line sensors are physically spaced apart from each other.

The thus read original document image is handled as image data differentfrom one another read by the respective reading line sensors, and theresultant image data are separately stored in memories or other storagemedia illustrated in (d) and (e) of FIG. 15.

When the sensor unit 105 then moves and hence the light source moves,the position where each line sensor detects the original document imagechanges, as illustrated in (a) of FIG. 16. The line sensor 1304 thendetects image data illustrated in (b) of FIG. 16, and the line sensor1305 detects image data illustrated in (c) of FIG. 16.

The thus read original document image is handled as image data differentbetween the reading line sensors, and the resultant image data areseparately stored in memories or other storage media illustrated in (d)and (e) of FIG. 16.

Similarly, when the portion in the position illustrated in (a) of FIG.17 is read, the image data illustrated in (b) and (c) of FIG. 17 arestored in memories or other storage media illustrated in (d) and (e) ofFIG. 17.

Further, when the portion in the position illustrated in (a) of FIG. 18is read, the image data illustrated in (b) and (c) of FIG. 18 are storedin memories or other storage media illustrated in (d) and (e) of FIG.18.

Finally, all the portions of the original document image are illuminatedwith the light from the light source, and the line sensors in therespective positions read image data.

The thus read image data are sequentially stored in the memories, andframe image data corresponding to a plurality of frames are acquired asillustrated in (a) and (b) of FIG. 19, the two sets of image datashifted by a single pixel in the secondary scan direction.

Each set of the frame image data shifted in the secondary scan directionis comprised of subsets of image data corresponding to the number ofline sensors, each of which being comprised of a set of pixel sensors.

Thus using an area sensor in which pixel sensors are arrangedtwo-dimensionally to read an image allows frame image data correspondingto a plurality of frames the phase of which is successively shifted inthe secondary scan direction to be obtained in a single reading action.

How to use the area sensor described above in the apparatus used in thepresent embodiment will be described below.

First, the area sensor illustrated in FIG. 13 is fixed in an inclinedposition in the reader.

(a) of FIG. 20 illustrates an example of how the area sensor is fixed inthe present embodiment. (a) of FIG. 20 illustrates an area sensor device2001 and pixel sensors 2002. In the following description, it is assumedthat the area sensor device is comprised of 20 pixel sensors in thelong-side direction and 10 pixel sensors in the short-side direction.

The area sensor is inclined to the reference installation position andthen fixed. That is, when the area sensor is fixed in the referenceinstallation position as illustrated in (a) of FIG. 20, the lowermostline sensor in the area sensor and the reference installation positionforms an angle θ.

The position of each of the constituent pixel sensors is expressed in acoordinate system defined by the origin being the upper left point ofthe area sensor, the x direction being the long-side direction, and they direction being the short-side direction. That is, the coordinates ofthe upper left point (x, y) is (0, 0), and the coordinates of the upperright point (x, y) is (19, 0). Similarly, the coordinates of the lowerleft point (x, y) is (0, 9), and the coordinates of the lower rightpoint (x, y) is (19, 9).

An area 2003 indicates a set of pixel sensors corresponding to a singleline that forms the area sensor 2001. Specifically, the single line iscomprised of 20 pixel sensors along the long-side direction.

That is, the single line is comprised of the pixel sensors in thecoordinates (0, 4), (1, 4), (2, 4), . . . (19, 4). In the followingdescription, a plurality of pixel sensors in the area 2003 is referredto as a reading line sensor 2003.

Similarly, an area 2004 includes pixel sensors in the coordinates (0,5), (1, 5), (2, 5), . . . (19, 5), and is referred to as a reading linesensor 2004 in the following description.

In the present embodiment, the reading unit 105 including the areasensor 113 fixed in the reader is moved in the direction indicated bythe arrow illustrated in FIG. 1 to read an original document imageplaced on the platen 104.

That is, the reading line sensors 2003 and 2004, each of which is a setof pixel sensors, are used as the line sensors to carry out reading asdescribed above.

How to process image data read by the reading line sensors 2003 and 2004will be described below. FIG. 14 illustrates an original document imageto be read in the following description. That is, the original documentimage corresponds to the original document image 103 illustrated in FIG.1.

The grid illustrated in FIG. 14 corresponds to the resolution of thepixel sensors that form one of the reading line sensors 2003 and 2004.Although the original document image is read in the same manner asillustrated in (a), (b), (c), (d) and (e) of FIGS. 15 to 19 describedabove, frame image data inclined by the angle θ is obtained because thearea sensor is inclined by θ.

For example, when the area sensor is not originally inclined, theposition indicated by the hatched portion illustrated in (a) of FIG. 21should be read. Since the area sensor is inclined, however, the linesensors 2003 and 2004 detect image data inclined as illustrated in (b)and (c) of FIG. 21.

The inclined image data are then stored as they are in memories or otherstorage media illustrated in (d) and (e) of FIG. 21. Similarly, when thesensor unit 105 moves and hence the light source moves, the positionindicated by the hatched portion illustrated in (a) of FIG. 22 is read.In this case, the line sensors 2003 and 2004 detect image data asillustrated in (b) and (c) of FIG. 22.

The image data are then stored in memories or other storage mediaillustrated in (d) and (e) of FIG. 22. Further, when the reading unitmoves in the secondary scan direction and hence the light source movesto read the position indicated by the hatched portion illustrated in (a)of FIG. 23, the line sensors 2003 and 2004 obtain image data illustratedin (b) and (c) of FIG. 23. The image data are then stored in memories orother storage media illustrated in (d) and (e) of FIG. 23.

(a) and (b) of FIG. 24 show frame image data finally detected and readby the line sensors 2003 and 2004. The thus read image data are thoseinclined by the angle θ. The direction indicated by the arrow (A) in (a)of FIG. 24 is referred to as the primary scan direction, and thedirection indicated by the arrow (B) is referred to as the secondaryscan direction. On the other hand, the direction indicated by the arrow(C) is referred to as the transverse direction of read image data. Thedirection indicated by the arrow (D) is referred to as the longitudinaldirection of the read image data.

As illustrated in (a) of FIG. 20, the reading line sensors 2003 and 2004are physically spaced apart from each other in the secondary scandirection by a single pixel. There is therefore a shift in phase in thelong-side direction between the pixel sensors that form the reading linesensor 2003 and the pixel sensors that form the reading line sensor2004.

For example, the pixel sensor in the reading line sensor 2003 that ispositioned in the coordinates (x, y)=(15, 4) is shifted from the pixelsensor in the reading line sensor 2004 that is positioned in thecoordinates (x, y)=(15, 5) by one unit step (y=1) in the y direction,which is the short-side direction. This shift causes a shift Δβ in thevertical direction in the reference installation position. On the otherhand, the positions of the two pixel sensors in the x direction, whichis the long-side direction, are the same, which is x=15. The inclinationangle θ, however, causes a shift in phase between the two pixel sensorsby a minute amount Δα, which is less than or equal to a sub-pixel, inthe horizontal direction in the reference installation position.

That is, when the area sensor is inclined, a minute shift in phaseoccurs even for pixel sensors in the same position in the x-axisdirection, which is the short-side direction, in a reading line sensor.The offset amount depends on the inclination angle. Image data read byreading line sensors defined in the area sensor 113 are therefore frameimage data different in terms of shift in phase between the reading linesensors. Specifically, the read image data illustrated in (a) of FIG. 24and the read image data illustrated in (b) of FIG. 24 are shifted fromeach other in terms of phase by a single pixel in the transversedirection, that is, not only by Δβ in the secondary scan direction butalso by Δα in the primary scan direction.

The above description has been made by assuming that there are tworeading line sensors (reading line sensors 2003 and 2004), but thepresent invention is not limited thereto. The number of pixel sensorsthat form the area sensor 113 may be increased in the short-sidedirection to form a large number of reading line sensors. That is, thenumber of reading line sensors can be increased up to the number ofpixels that form the area sensor 113.

The number of thus adapted reading line sensor is equal to the number offrame image data sets obtained in a single reading action. That is,forming reading line sensors corresponding to 30 lines in the areasensor 113 allows frame image data sets corresponding to 30 frames, eachof which having its own shift in phase, to be obtained in a singlereading action.

When the area sensor is inclined, frame image data sets can be obtainedin a single scan action by shifting the position of an original documentimage to be read by sensors adjacent in the short-side direction by ashift of less than one pixel in the primary and secondary scandirections. Using frame image data obtained by such reading controlalong with the super-resolution processing therefore allows formation ofimage data the resolution of which is higher than that of the readingdevice.

In addition to the sensor arrangement as discussed above, anotherarrangement is possible as shown in (b) of FIG. 20. As is in thearrangement of (a) of FIG. 20, when the area sensor is inclined, frameimage data sets can be obtained in a single scan action by shifting theposition of an original document image to be read by sensors adjacent inthe short-side direction by a shift of less than one pixel in theprimary and secondary scan directions.

Namely, it is sufficient to move the scan position in parallel relativeto an original document image in an area sensor comprising a pluralityof sensors in order to obtain frame image data sets by shifting theposition of the original document image to be read by sensors adjacentin the short-side direction by a shift of less than one pixel in theprimary and secondary scan directions. In addition, it is possible togain more frame image data that can be obtained in the sensor short-sidedirection by increasing the number of readings of the original documentimage in the secondary scan direction and increasing the number ofsamplings per unit time.

Embodiments will be described below based on the configuration describedabove.

(First Embodiment)

First, the procedure of the present embodiment will be described withreference to FIG. 25. In the procedure, reading pixel sensors diagonallypositioned with respect to a reference installation position are used toread an original document image to acquire frame image datacorresponding to a plurality of frames different from one another interms of phase, and the resultant frame image data is used to performhigh-resolution processing.

In FIG. 25, upon initiation of an original document image readingprocess, in the step S2501, the area sensor diagonally positioned withrespect to a reference installation position is used to read an originaldocument image.

The original document image reading process is initiated when the userplaces the original document image on one of the glass platen and theADF and pushes a start button, as in a typical copy process.

Image data obtained by the diagonally positioned area sensor islow-resolution frame image data read by line sensors formed in the areasensor, as described above.

When the original document image is scanned once, one-frame image datais obtained by each of the line sensors. In the process of reading imagedata by line sensors adjacent to each other in the short-side direction,it is possible to read frame image data corresponding to a plurality offrames shifted in the primary scan direction by a shift of less than onepixel.

Since the area sensor is inclined by θ, each of the read frame imagedata sets is also inclined by θ.

In the next step S2502, inclination angle information on the inclinedread frame image data that has been read is obtained.

That is, the inclination angle of the area sensor is acquired. Theinclination angle θ can be acquired in a process of assembling amultifunction peripheral including the area sensor at the point when thearea sensor 113 is fixed in the reading unit 105.

The inclination angle θ is held as a value specific to thearea-sensor-fixed apparatus in a storage area in the multifunctionperipheral. The angular information is acquired from the storage area inthe multifunction peripheral.

In the next step S2503, the angular information is used to performaffine transformation so as to rotate the inclined frame image data thathas been acquired. In this process, the frame image data is rotated bythe inclination angle. This operation corrects the inclination of theframe image data. Let (X, Y) be the coordinates before thetransformation, (X′, Y′) be the coordinates after the transformation,and θ be the angle of rotation (the inclination angle of the area sensorin the present embodiment). The affine transformation expressed by theFormula 1 is then used to provide inclination-corrected frame imagedata.

$\begin{matrix}{\left\lbrack {X^{\prime},Y^{\prime}} \right\rbrack = {\left\lbrack {X,Y} \right\rbrack\begin{bmatrix}{\cos\;\theta} & {\sin\;\theta} \\{{- \sin}\;\theta} & {\cos\;\theta}\end{bmatrix}}} & \left( {{Formula}\mspace{14mu} 1} \right)\end{matrix}$

-   -   X′, Y′: Coordinates after transformation    -   X, Y: Coordinates before transformation

The frame image data obtained by performing the affine transformation isinclination-corrected low-resolution frame image data.

The method for correcting the inclination is not limited to affinetransformation, but may be any other method for correcting theinclination of image data.

In the step S2504, the plurality of inclination-free frame image data isused to perform super-resolution conversion, which is high-resolutionconversion in the process described above, and image data the resolutionof which is higher than the resolution of the sensor provided in theapparatus is output.

In the step S2505, the resultant image data is printed on a sheet ofpaper as an output. The inclination may be alternatively corrected afterthe super-resolution conversion is performed.

(Second Embodiment)

In the first embodiment, the inclination angle θ is acquired from avalue that can be acquired when the area sensor 113 is fixed in thereading unit 105 in the process of assembling a multifunction peripheralincluding the area sensor.

In the present embodiment, the inclination angle is not acquired fromexisting information stored in the apparatus, but the inclination angleinformation is acquired by detecting the inclination of the area sensorwhen the apparatus receives an instruction from the user.

A method for detecting the inclination of the area sensor will bedescribed with reference to FIG. 26, (a) of FIG. 27 and (b) of FIG. 27.The process of determining the inclination of the area sensor in thepresent embodiment uses a method for acquiring deviation smaller than asingle pixel by searching pixel sensors outputting high read densityvalues among the pixel sensors that have read a straight line having awidth corresponding to a single pixel in the area sensor and evaluatingthe density values of the pixels around each of the pixel sensorsoutputting high read density values.

FIG. 26 illustrates an example of a test chart used to detect theinclination of the fixed area sensor.

A number of straight lines are drawn on the test chart, each of thestraight lines having a width corresponding to a single pixel in thearea sensor.

The straight lines are drawn parallel to each other on the originaldocument image. When the original document image is read, the originaldocument image is placed on the platen parallel to the secondary scandirection. In this case, a mark or any other similar indication may beprovided on the platen so that the reading is carried out with thestraight lines being parallel to the secondary scan direction. When thechart is read, and a certain single pixel sensor is looking at asolidly-painted portion (the read density value of the pixel sensor is100%), each of the pixel sensors on the right and left sides of thatpixel sensor (in the long-side direction) should be looking at a portionin which the read density value of the pixel sensor is 0%. It is notedthat a read density value greater than a certain threshold value may beconsidered to be a read density value of 100%, although depending on theperformance of the sensor. Similarly, a read density value smaller thana certain threshold value may be considered to be a read density valueof 0%.

Thus reading a printed straight line allows the position where thestraight line is drawn in the original document image to be readilydetected.

When no solidly-painted portion is detected from a pixel sensor, thatis, the pixel sensor does not output a read density value of 100%,detecting the read density values of the pixel sensors on the right andleft sides of that pixel sensor allows determination of how much a linehaving a width corresponding to a single pixel is inclined within thesame pixel sensor. Now assume that a read density value is proportionalto the area of a pixel sensor used to read an original document image(solidly-painted portion).

Based on the above assumption, for example, when a certain pixel sensoroutputs a read density value of 50%, half the pixel sensor is looking ata solidly-painted portion, and hence the pixel sensor should be deviatedfrom the straight line on the test chart by half a single pixel.

Similarly, when a certain pixel sensor outputs a read density value of20%, one-fifth the pixel sensor is looking at a solidly-painted portion,and hence the pixel sensor should be deviated by one-fifth a singlepixel.

While it is assumed that the thickness of the straight line on the testchart is equal to the width corresponding to a single pixel for the sakeof simplification, the thickness of the line is not necessarily thewidth corresponding to a single pixel.

Checking the density values of the surrounding pixels around a pixelthat reads a straight line allows the position where the straight lineis drawn in a single pixel sensor to be detected.

(a) and (b) of FIG. 27 is a diagram illustrating how the diagonallypositioned area sensor reads a straight line having a widthcorresponding to a single pixel and detects the angle of the sensor. In(a) of FIG. 27, a straight line 2701 has a width corresponding to asingle pixel and is drawn on a test chart.

Pixel sensors 2702 and 2703 are not adjacent to each other, but arrangedon the straight line on the test chart with a few pixel sensorstherebetween.

The pixel sensors 2702 and 2703 represent pixel sensors that have readthe straight line 2701 having a width corresponding to a single pixeland output a read density value of 100% (or a read density valueconsidered to be 100%).

Now, let A be the center of the pixel sensor 2703, B be the center ofthe pixel sensor 2702, and θ be the inclination of the area sensor.

Considering the distance between A and B, in (a) of FIG. 27, since thedistance in the long-side direction corresponds to a single pixel andthe distance in the short-side direction corresponds to four pixels, X=Nand Y=4L.

In (a) of FIG. 27, since each of the pixel sensors is drawn as a circle,N=L, but other definitions are made for pixel sensors that are notcircular. The distance between pixel sensors is expressed by N.

When each of the pixel sensors 2702 and 2703 outputs a read densityvalue of 100% as illustrated in (a) of FIG. 27, the distance between thepixel sensors can be used to calculate the angle of the sensor by usingthe following formula.θ=arc tan(X/Y)X=NY=4L

Instead of detecting two or more sensors outputting a read density valueof 100% on the straight line 2701 on the test chart, sensors outputtingread density values that are considered to be the same density value maybe detected.

Now, consider a case different from the case illustrated in (a) of FIG.27. That is, as illustrated in (b) of FIG. 27, assume that neither oftwo pixel sensors can output a read density value of 100% when reading astraight line having a width corresponding to a single pixel.

Alternatively, assume that two pixel sensors cannot output a readdensity value considered to be the same when reading a straight linehaving a width corresponding to a single pixel. In this case, two pixelsensors that read a straight line having a width corresponding to asingle pixel and output substantially the same read density values maybe detected. A straight line 2704 has a width corresponding to a singlepixel.

A pixel sensor 2705 represents a pixel sensor that has read a straightline having a width corresponding to a single pixel and output a readdensity value of 100%.

The pixel sensor 2705 illustrated in FIG. 27( b) reads the straight line2704 and outputs a read density value of 100%. However, a pixel sensor2706 positioned on the straight line 2704 read by the pixel sensor 2705does not output a read density value of 100% when reading the straightline 2704.

Now, let A be the center of the pixel sensor 2706, and B′ be theintersection of the line extending from the pixel sensor 2706 toward thepixel sensor 2705 in the vertical direction, that is, the direction inwhich the straight line 2704 extends, and the line passing through thecenter of the pixel sensor 2705 and extending in the long-sidedirection.

Let a be the length between the center of the pixel sensor 2705 and B′,and θ′ be the inclination of the area sensor.

As described above, since the read density value of a sensor isproportional to the area of the sensor used to read an image, “theamount of deviation α” is also proportional to the read density value ofthe sensor.

For example, when the read density value is 100%, α=0. When the readdensity value is 90%, α=0.1N. When the read density value is 10%,α=0.9N.

In this case, when the deviation is smaller than a single pixel, thecalculation can be carried out by using the following formulas inconsideration of the distance between the two pixel sensors and theamount of deviation α in the long-side direction.θ′=arc tan(X/Y)X=N+αY=4LThe inclination angle of the area sensor can be thus determined. Asillustrated in (a) and (b) of FIG. 27, the inclination of the areasensor can be calculated by detecting the read density values of two ormore pixel sensors located on a straight line or in the vicinity of astraight line.

FIG. 28 is a flowchart describing an area sensor inclination angleacquiring unit in the present embodiment. In the present process, whenan instruction is received from the user, the CPU (301) initiates thedetection of the inclination of the area sensor. First, in the stepS2801, a test chart placed on the platen is scanned.

The image illustrated in FIG. 26 is used as the test chart to bescanned. The test chart may be output from the same MFP as that fordetermining the inclination angle of the area sensor or output fromanother printing apparatus.

In the next step S2802, pixel sensors in the sensor that read a straightline on the test chart and output read density values considered to bethe same value are searched and sorted.

The details of the above operation have been already described withreference to (a) and (b) of FIG. 27.

In the next step S2803, as having been illustrated in (a) of FIG. 27, itis determined whether there is a plurality of pixel sensors that hasread a single straight line on the test chart and output read densityvalues considered to be the same value.

When there is a plurality of such pixel sensors, the straight line onthe test chart should pass through the centers of the pixel sensors. Theinclination angle of the area sensor is therefore acquired from thedistance between the pixel sensors (step S2808).

On the other hand, in the step S2803, when there is not a plurality ofpixel sensors that have read a single straight line and output densityvalues considered to be the same value as illustrated in (b) of FIG. 27,the control proceeds to the step S2804.

The density values of the pixel sensors adjacent to each other in thelong-side direction are used to acquire the amount of deviation a fromthe line that is smaller than a single pixel.

In the next step S2805, the amount of deviation a acquired in the stepS2804 is added in the long-side direction, and the inclination angle ofthe area sensor is acquired in consideration of the amount of deviationa smaller than a single pixel.

It is determined whether the inclination angle of the area sensoracquired in the step S2805 is greater than a threshold value (stepS2806). When the inclination angle is greater than the threshold value,an error is displayed (step S2809).

The reason of displaying an error is that when the inclination angle isgreater than the threshold value, the shift in phase between read frameimage data adjacent to each other will not be small enough. In thiscase, frame image data necessary to perform super-resolution processingcannot be obtained.

When the inclination angle of the area sensor acquired in the step S2805is not greater than the threshold value, the inclination angle of thearea sensor is stored in a secondary storage device, such as an NVRAM(step S2807), and the process is terminated. The above operationcorresponds to the step S2502 in FIG. 25.

The configuration in the present embodiment allows multiple sets offrame image data different from one another in terms of shift in phaseon the order of sub-pixel to be obtained in a single scan action withoutmajor change in conventional configuration.

The inclination angle information acquiring unit described above is thenused to correct the inclination of the resultant frame image data, asdescribed in the first embodiment, and the corrected frame image data isused to perform the high-resolution processing described above. Ahigh-resolution image can be thus provided.

(Third Embodiment)

In the second embodiment, the process of determining the inclination ofan area sensor has been described. The process uses a method foracquiring deviation smaller than a single pixel by searching pixelsensors outputting high read density values among the pixel sensors thathave read a straight line having a width corresponding to a single pixeland evaluating the density values of the pixels around each of the pixelsensors outputting high read density values.

In the present embodiment, an area sensor inclination angle informationacquiring unit different from that in the second embodiment will bedescribed.

As illustrated in FIG. 29, when the user places a straight line having awidth corresponding to a single pixel that is drawn parallel to thesecondary scan direction and the area sensor reads the straight line,the amount of change in density of pixels in a row where the densitycontinuously changes in the Y-axis direction is used to acquire theinclination angle of the area sensor.

FIG. 29 is a diagram describing a process of acquiring the inclinationof the area sensor by using the sensor to read a straight line having awidth corresponding to a single pixel and finding an edge of thestraight line. FIG. 29 illustrates a straight line 2901 having a widthcorresponding to a single pixel, pixel sensors 2902 to 2906 in a row m,and a pixel sensor 2907 in a row (m+1).

Now, let X be the distance between pixel sensors in the long-sidedirection, and Y be an edge distance in the short-side direction. Theinclination angle can be acquired by using the following formula, whichis similar to that in the first embodiment.θ=arc tan(X/Y)

In FIG. 29, for example, the pixel sensor 2902 is located on thestraight line having a width corresponding to a single pixel, andoutputs a read density value of 100%. Similarly, the pixel sensors 2903,2904, 2905, 2906, and 2907 output read density values of 70%, 40%, 10%,0%, and 80%, respectively. As described above, the read density value isproportional to the amount of deviation α.

In this case, the density detected by each of the sensors changes by30%. That is, the rate of change in the amount of deviation α is 30%.The rate of change corresponds to the inclination of the straight lineon the test chart. That is, the inclination is 0.3.

X and Y can be determined in consideration of the relationship betweenthe pixel sensors 2903 and 2904. In this case, the amount of change X inthe X-axis direction from the center of the pixel sensor 2903 to thecenter of the pixel sensor 2904 is 0.3N, and the amount of change Y inthe Y direction is L. The inclination angle can be determined by usingthe formula θ=arc tan(0.3N/L).

Similarly, X and Y can be determined in consideration of therelationship between the pixel sensors 2903 and 2906. In this case, theamount of change X in the long-side direction is 1.2N, and the amount ofchange Y in the short-side direction is 4L. The inclination angle can bedetermined by using the formula θ=arc tan(1.2N/4L), leading to the sameresult.

The configuration of the pixel sensors in the present embodiment allowsthe inclination of the area sensor to be detected by detecting an edge.The inclination of the area sensor can therefore be detectedirrespective of the width of a straight line used on the test chart.That is, even in an output apparatus that can hardly print a widthcorresponding to a single pixel, the inclination of the area sensor canbe correctly detected.

As a result, a super-resolution image can be precisely formed by usingcorrect angular information.

(Fourth Embodiment)

In the second and third embodiments, the area sensor inclination angleacquiring unit initiates its operation when the user issues an executioninstruction and the CPU receives the instruction.

That is, once inclination angle information is acquired and the resultis stored in the secondary storage device, the apparatus uses the storedinclination angle information to perform high-resolution conversionuntil the apparatus receives another instruction to acquire angularinformation.

In the present embodiment, the inclination angle acquiring unit isinitiated when the number of scans, each of which is the reading actionusing the sensor, becomes greater than a certain number.

When the number of reading actions carried out by the apparatus reachesa number specified by one of the user and an administrator, theinclination angle acquiring unit is initiated. The number specified bythe user is arbitrarily set.

For example, the certain number may be set to one. In this case, theinclination of the area sensor is detected for each scan action.

That is, the inclination angle is acquired before the high-resolutionconversion is performed even when the user issues no instruction. It isthus possible to handle change in inclination angle of the area sensordue to change over time.

Further, for example, when a repair person replaces a malfunctioningarea sensor with a new one, the process described above may be carriedout.

As described above, the present embodiment can prevent degradation inhigh-resolution performance and inclination of an image caused by changeover time, resulting in a configuration unlikely affected by change overtime.

Further, when the acquired inclination angle θ is greater than athreshold value due to change over time, a warning may be issued to theuser to prompt the user to carry out maintenance actions.

The threshold value in this case is the inclination angle of the areasensor when the reading position where pixel sensors adjacent to eachother in the short-side direction read image data is shifted by a singlepixel or greater in the primary scan direction.

In this case, since the condition “the shift of the reading positionwhere pixel sensors adjacent to each other in the short-side directionread an original document image should be smaller than a single pixel inthe primary scan direction,” which is a condition necessary to carry outsuper-resolution processing, that is high-resolution processing, cannotbe satisfied, appropriate super-resolution processing cannot be carriedout.

(Other Embodiments)

The scope of the embodiments described above encompasses a method forstoring a program on a storage medium, the program operating theconfiguration of any of the embodiments described above to achieve thefunctions of the embodiment, reading the program, as codes, stored inthe storage medium, and executing the codes in a computer. Further, notonly the storage medium on which the program is stored but also theprogram itself are encompassed in the embodiments described above.

Examples of the storage medium may include a floppy disk, a hard disk,an optical disk, a magneto-optical disk, a CD-ROM, a magnetic tape, anon-volatile memory card, and a ROM.

The scope of the embodiments described above encompasses not only thosethat use a program alone stored on any of the storage medium describedabove to carry out processes but also those operate on an OS incooperation with other software and the function of an expansion boardto carry out the actions in the embodiments described above.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application Nos.2007-330977, filed Dec. 21, 2007 and 2008-317282, filed Dec. 12, 2008,which are hereby incorporated by reference herein in their entirety.

The invention claimed is:
 1. An image processing apparatus comprising:an area sensor unit configured to read image data corresponding to aplurality of frames shifted from each other by a shift of less than onepixel; an inclination angle acquiring unit configured to acquire aninclination angle with respect to a reference installation position ofthe area sensor; an angle correcting unit configured to correct theinclination of the image data corresponding to a plurality of framesread by the area sensor unit by using the inclination angle acquired bythe inclination angle acquiring unit; and a high-resolution conversionunit configured to provide image data the resolution of which is higherthan the resolution of the read image data by using the image datacorresponding to a plurality of frames the inclination of which has beencorrected by the angle correcting unit to perform interpolationprocessing.
 2. The image processing apparatus according to claim 1,wherein when the area sensor unit is used to read a straight line drawnon an original document image, the inclination angle acquiring unitacquires the inclination angle by detecting read density values of twosensor components for a pixel, among sensor components for a pixel thatform the area sensor, on the straight line and calculating theinclination angle of the area sensor.
 3. The image processing apparatusaccording to claim 1, wherein whenever the area sensor unit reads anoriginal document image arbitrarily determined times, the inclinationangle is acquired.
 4. The image processing apparatus according to claim2, wherein whenever the area sensor unit reads an original documentimage arbitrarily determined times, the inclination angle is acquired.5. The image processing apparatus according to claim 1, furthercomprising a warning unit configured to warn a user when the angleacquired by the inclination angle acquiring unit is greater than athreshold value so that the area sensor unit cannot read image datacorresponding to a plurality of frames shifted from each other by ashift of less than one pixel.
 6. The image processing apparatusaccording to claim 2, further comprising a warning unit configured towarn a user when the angle acquired by the inclination angle acquiringunit is greater than a threshold value so that the area sensor unitcannot read image data corresponding to a plurality of frames shiftedfrom each other by a shift of less than one pixel.
 7. The imageprocessing apparatus according to claim 3, further comprising a warningunit configured to warn a user when the angle acquired by theinclination angle acquiring unit is greater than a threshold value sothat the area sensor unit cannot read image data corresponding to aplurality of frames shifted from each other by a shift of less than onepixel.
 8. The image processing apparatus according to claim 4, furthercomprising a warning unit configured to warn a user when the angleacquired by the inclination angle acquiring unit is greater than athreshold value so that the area sensor unit cannot read image datacorresponding to a plurality of frames shifted from each other by ashift of less than one pixel.
 9. An image processing apparatuscomprising: an area sensor unit configured to read image datacorresponding to a plurality of frames shifted from each other by ashift of less than one pixel; a high-resolution conversion unitconfigured to provide image data the resolution of which is higher thanthe resolution of the read image data by using the image datacorresponding to a plurality of frames read by the area sensor unit toperform interpolation processing; an inclination angle acquiring unitconfigured to acquire an inclination angle indicating the inclinationwith respect to a reference installation position of the area sensor;and an angle correcting unit configured to correct the inclination ofthe high-resolution image data acquired by the high-resolutionconversion unit by using the inclination angle acquired by theinclination angle acquiring unit.
 10. The image processing apparatusaccording to claim 9, wherein when the area sensor unit is used to reada straight line drawn on an original document image, the inclinationangle acquiring unit acquires the inclination angle by detecting readdensity values of two sensor components for a pixel, among sensorcomponents for a pixel that form the area sensor, on the straight lineand calculating the inclination angle of the area sensor.
 11. The imageprocessing apparatus according to claim 9, wherein whenever the areasensor unit reads an original document image arbitrarily determinedtimes, the inclination angle is acquired.
 12. The image processingapparatus according to claim 10, wherein whenever the area sensor unitreads an original document image arbitrarily determined times, theinclination angle is acquired.
 13. The image processing apparatusaccording to claim 9, further comprising a warning unit configured towarn a user when the angle acquired by the inclination angle acquiringunit is greater than a threshold value so that the area sensor unitcannot read image data corresponding to a plurality of frames shiftedfrom each other by a shift of less than one pixel.
 14. The imageprocessing apparatus according to claim 10, further comprising a warningunit configured to warn a user when the angle acquired by theinclination angle acquiring unit is greater than a threshold value sothat the area sensor unit cannot read image data corresponding to aplurality of frames shifted from each other by a shift of less than onepixel.
 15. The image processing apparatus according to claim 11, furthercomprising a warning unit configured to warn a user when the angleacquired by the inclination angle acquiring unit is greater than athreshold value so that the area sensor unit cannot read image datacorresponding to a plurality of frames shifted from each other by ashift of less than one pixel.
 16. The image processing apparatusaccording to claim 12, further comprising a warning unit configured towarn a user when the angle acquired by the inclination angle acquiringunit is greater than a threshold value so that the area sensor unitcannot read image data corresponding to a plurality of frames shiftedfrom each other by a shift of less than one pixel.
 17. An imageprocessing method used in an image processing apparatus including anarea sensor unit that reads image data corresponding to a plurality offrames shifted from each other by a shift of less than one pixel, themethod comprising the steps of: acquiring an inclination angle withrespect to a reference installation position of the area sensor;correcting the inclination of the image data corresponding to aplurality of frames read by the area sensor unit by using theinclination angle acquired in the inclination angle acquiring step; andproviding image data the resolution of which is higher than theresolution of the read image data by using the image data correspondingto a plurality of frames the inclination of which has been corrected inthe angle correcting step to perform interpolation processing.
 18. Theimage processing method according to claim 17, wherein when the areasensor unit is used to read a straight line drawn on an originaldocument image, the inclination angle acquiring step is used to acquirethe inclination angle by detecting read density values of two sensorcomponents for a pixels, among sensor components for a pixels that formthe area sensor, on the straight line and calculating the inclinationangle of the area sensor.
 19. The image processing method according toclaim 17, wherein whenever the area sensor unit reads an originaldocument image arbitrarily determined times, the inclination angle isacquired.
 20. The image processing method according to claim 18, whereinwhenever the area sensor unit reads an original document imagearbitrarily determined times, the inclination angle is acquired.
 21. Theimage processing method according to claim 17, further comprisingwarning a user when the angle acquired in the inclination angleacquiring step is greater than a threshold value so that the area sensorunit cannot read image data corresponding to a plurality of framesshifted from each other by a shift of less than one pixel.
 22. The imageprocessing method according to claim 18, further comprising warning auser when the angle acquired in the inclination angle acquiring step isgreater than a threshold value so that the area sensor unit cannot readimage data corresponding to a plurality of frames shifted from eachother by a shift of less than one pixel.
 23. The image processing methodaccording to claim 19, further comprising warning a user when the angleacquired in the inclination angle acquiring step is greater than athreshold value so that the area sensor unit cannot read image datacorresponding to a plurality of frames shifted from each other by ashift of less than one pixel.
 24. The image processing method accordingto claim 20, further comprising warning a user when the angle acquiredin the inclination angle acquiring step is greater than a thresholdvalue so that the area sensor unit cannot read image data correspondingto a plurality of frames shifted from each other by a shift of less thanone pixel.
 25. An image processing method used in an image processingapparatus including an area sensor unit that reads image datacorresponding to a plurality of frames shifted from each other by ashift of less than one pixel, the method comprising the steps of:providing image data the resolution of which is higher than theresolution of the read image data by using the image data correspondingto a plurality of frames read by the area sensor unit to performinterpolation processing; acquiring an inclination angle indicating theinclination with respect to a reference installation position of thearea sensor; and correcting the inclination of the high-resolution imagedata acquired in the high-resolution conversion step by using theinclination angle acquired in the inclination angle acquiring step. 26.The image processing method according to claim 25, wherein when the areasensor unit is used to read a straight line drawn on an originaldocument image, the inclination angle acquiring step is used to acquirethe inclination angle by detecting read density values of two sensorcomponents for a pixel, among sensor components for a pixel that formthe area sensor, on the straight line and calculating the inclinationangle of the area sensor.
 27. The image processing method according toclaim 25, wherein whenever the area sensor unit reads an originaldocument image arbitrarily determined times, the inclination angle isacquired.
 28. The image processing method according to claim 26, whereinwhenever the area sensor unit reads an original document imagearbitrarily determined times, the inclination angle is acquired.
 29. Theimage processing method according to claim 25, further comprisingwarning a user when the angle acquired in the inclination angleacquiring step is greater than a threshold value so that the area sensorunit cannot read image data corresponding to a plurality of framesshifted from each other by a shift of less than one pixel.
 30. The imageprocessing method according to claim 26, further comprising warning auser when the angle acquired in the inclination angle acquiring step isgreater than a threshold value so that the area sensor unit cannot readimage data corresponding to a plurality of frames shifted from eachother by a shift of less than one pixel.
 31. The image processing methodaccording to claim 27, further comprising warning a user when the angleacquired in the inclination angle acquiring step is greater than athreshold value so that the area sensor unit cannot read image datacorresponding to a plurality of frames shifted from each other by ashift of less than one pixel.
 32. The image processing method accordingto claim 28, further comprising warning a user when the angle acquiredin the inclination angle acquiring step is greater than a thresholdvalue so that the area sensor unit cannot read image data correspondingto a plurality of frames shifted from each other by a shift of less thanone pixel.
 33. A non-transitory computer readable medium that stores aprogram that causes an image processing apparatus including an areasensor unit that reads image data corresponding to a plurality of framesshifted from each other by a shift of less than one pixel to perform thesteps of: acquiring an inclination angle with respect to a referenceinstallation position of the area sensor; correcting the inclination ofthe image data corresponding to a plurality of frames read by the areasensor unit by using the inclination angle acquired in the inclinationangle acquiring step; and providing image data the resolution of whichis higher than the resolution of the read image data by using the imagedata corresponding to a plurality of frames the inclination of which hasbeen corrected in the angle correcting step to perform interpolationprocessing.
 34. A non-transitory computer readable medium that stores aprogram that causes an image processing apparatus including an areasensor unit that reads image data corresponding to a plurality of framesshifted from each other by a shift of less than one pixel to perform thesteps of: providing image data the resolution of which is higher thanthe resolution of the read image data by using the image datacorresponding to a plurality of frames read by the area sensor unit toperform interpolation processing; acquiring an inclination angleindicating the inclination with respect to a reference installationposition of the area sensor; and correcting the inclination of thehigh-resolution image data acquired in the high-resolution conversionstep by using the inclination angle acquired in the inclination angleacquiring step.